为什么在 SortedSet 中查找 headSet 时附加空字符“\0”？

Question

这个成语是什么意思？与“\0”连接的 java 字符串（例如 "Japan[=17=]"）？如

SortedSet<String> countryHeadSet 
    = countrySet.headSet("Japan[=10=]");

字符串"Japan[=12=]"在调用中是什么意思？如果程序员只写

会有什么不同吗

countryHeadSet 
    = countrySet.headSet("Japan");

Answer 1

我找到了答案。感谢所有的想法。

一个字符串的成语用法之一"[=13=]"，尤其是当你看到它的时候用一个range-view操作一个SortedSet，就是用它来找到 字符串的后继。

需要这样的继任者，因为那些 range-view 操作（subSet() , headSet(), 和 tailSet()) 提供 half-open 间隔, 你可能需要字符串的后继来构造一个 closed 区间。 Java Doc of Sorted Set

中对此进行了解释

Several methods return subsets with restricted ranges. Such ranges are half-open, that is, they include their low endpoint but not their high endpoint (where applicable). If you need a closed range (which includes both endpoints), and the element type allows for calculation of the successor of a given value, merely request the subrange from lowEndpoint to successor(highEndpoint). For example, suppose that s is a sorted set of strings. The following idiom obtains a view containing all of the strings in s from low to high, inclusive:

SortedSet sub = s.subSet(low, high+"[=21=]");

也就是说下面两个调用的区别：

countrySet.headSet("Japan[=10=]");
countrySet.headSet("Japan")

是第一个会得到countrySet中的所有字符串在从集合开头到包括的范围内字符串 "Japan" （即范围是封闭区间）；尽管第二个将获取范围内的所有字符串集合的开头，最多 但不包括 字符串 "Japan"（即范围是 half-open 区间）。

我包括一个我自己的测试程序来演示成语:

import java.util.Arrays;
import java.util.List;
import java.util.SortedSet;
import java.util.TreeSet;

public class StringPlusNull {

    public static void main(String[] args) {
        List<String> countryList 
            = Arrays.asList("U.S.", "U.K.", "China", "Japan", "Korea");
        SortedSet<String> countrySet
            = new TreeSet<>(countryList);

        String toElement = "Japan";
        SortedSet<String> countryHeadSet 
            = countrySet.headSet(toElement);
        System.out.format("There are %d countries in the "
                + "(half-open) headset [, %s): %s%n"
                , countryHeadSet.size(), toElement, countryHeadSet);

        toElement = "Japan[=11=]";
        countryHeadSet 
            = countrySet.headSet(toElement);
        System.out.format("There are %d countries in the "
                + "(half-open) headset [, %s): %s%n"
                , countryHeadSet.size(), toElement, countryHeadSet);
    }

}

输出将是：

There are 1 countries in the (half-open) headset [, Japan): [China]
There are 2 countries in the (half-open) headset [, Japan ): [China, Japan]

为什么在 SortedSet 中查找 headSet 时附加空字符“\0”？

Why append the null character "\0" when looking for a headSet in a SortedSet?

java

sortedset